The invention relates to the field of antennas, especially that of plasma antennas able to operate over a very wide frequency band.
Known antennas operate in a narrow frequency band and their size is inversely proportional to the operating wavelength.
In the low frequency (LF), very low frequency (VLF), and extremely low (ELF) ranges, the height of quarter-wave antennas must reach several hundred meters to several hundred kilometers, for example 750 km at 100 Hz, and their design becomes problematic. Moreover, it is far from easy to move them.
This frequency range is useful however, particularly when communicating with a submerged vessel such as a submarine.
To solve this problem, the use of plasma antennas is known.
Thus, U.S. Pat. No. 3,404,403 describes a plasma antenna having means for producing a laser beam, means for enabling this laser to be used in pulsed mode, means for focusing this laser beam on different spots to ionize an air column, and means for coupling a signal to the base of the air column.
U.S. Pat. No. 6,087,993 is also known; this describes an antenna having a vertical ionizing beam generator, and means for supplying the generator enabling a plasma column to be produced, the generator being able to produce a modulated current in the plasma. In addition, an electro-optical crystal is associated both with the laser beam and with a generator of a frequency-modulated signal. Thus, the crystal modulates the phase or amplitude of the laser, and this modulation directly affects the plasma column.